120 DR. J. STEPHEXSON ON THE MORPHOLOGY, CLASSIFICATION, 



on one or other or both sides of the septnm ; on reaching the 

 ventral body- wall it runs backwards for a short distance and 

 joins the prostate, a glandular mass in segm. x of cylindiical 

 or rounded shape, with a central lumen, which discharges to the 

 exterior in the groove between segms. x and xi. 



The ovaries are on the posterior face of septum 10/11, the 

 funnels on the anterior face of septum 11/12 ; the short oviducts 

 reach the surface in groove 11/12. A large pair of ovisacs — 

 backward pouchings of septum 11/1 2 — extend backwards through, 

 as a rule, several segments. The spermathecae are ovoid sacs 

 attached to the hinder face of septum 7/8 ; a winding duct leads 

 down the septum to the body-wall, and ends in the corresponding 

 groove ; just before it enters the body- wail there is often a 

 muscular sac, the spermathecal atrivim, of moderate size, or small, 

 or it may be even minute, connected with it. 



In the account which follows of the minuter structure of the 

 various organs, references will be made where necessary to the 

 previous work of Beddard (2, 3, 6, 7), Bourne (11), and Benham 

 (10), who used serial sections in their investigations, and to that 

 of Michaelsen, whose systematic papers (13, 14, 16) contain the 

 record of important anatomical details. 



(1) The Neplir'idia. 



The nephridia (PI. I. fig. 1) are attached to the posterior faces 

 of the septa; in the middle of the body each has a total length 

 of about 1 mm. 



Each is divisible on inspection into four portions : — (i.) The 

 anteseptal portion Avith the nephrostome ; (ii.) the twisted 

 nephridial tube; (iii.) larger than the last portion and more 

 dorsally situated, an oval and vertically elongated sac, occupying 

 the mid-lateral region as it lies on the body- wall in the dissection; 

 (iv.) projecting from the lower end of the sac is a stifl', straight 

 terminal duct. 



The nephrostome (??,) is 45-50 /x in diameter, and has a marginal 

 rosette of about 20 ciliated cells. 



From the nephrostome leads the nephrostomial canal («.c.), 

 8-10 //. in diameter, which pierces the septum, and after a straight 

 course of a bout 1 70 yu, becomes the spiral coil. 



The portion of the organ which was roughly distinguished 

 above as the twisted nephridial tube can be divided on closer 

 inspection into three parts, which may be named the spiral coil, 

 the twisted loop, and the spindle-shaped portion. The diameter 

 of the tube throughout this part of its course is 40-45 /x ; it is of 

 a slightly brownish colour. The lumen is wide, but intracellular 

 — bored through the middle of a single series of cells (drain- pipe 

 arrangement). The appearance of both longitudinal, transverse, 

 and optical sections is at first sight inisleading ; the drain-pipe 

 series of cells appears to be free within the lumen of a larger 



